Induction of sister-chromatid exchanges in cultured human cells by an organophosphorous insecticide: malathion.

Because malathion is a widely used organophosphorous insecticide, the effects of non-toxic concentrations (2.5--40 micrograms/ml) on sister-chromatid exchange (SCE) frequencies were determined. Human fetal fibroblasts were exposed once or twice to malathion, with 20 h between exposures. A single exposure to a concentration of 40 micrograms/ml resulted in a highly significant increase in the number of SCEs. After a double exposure, a concentration of 20 micrograms/ml induced an even greater increase in SCE frequencies. Comparison of Sce frequencies after single and double exposures indicated a cumulative effect; the number of exchanges at concentrations of 5 micrograms/ml or higher was significantly greater after the double exposure. An analysis of SCEs by chromosome group showed that exchanges were distributed approximately according to chromosome length.